One of the things we can struggle with in close-up
photography is a narrow depth of field. This is usually caused by shooting at a
wide aperture coupled with being fairly close to your subject. There are ways
around this without losing your pleasant blurred background or important detail: one of these
methods is focus stacking.

Focus stacking is taking more than one photo of the same
subject with a different part of the object in focus and combining them to make one photo. In this tutorial I’ll be
using Photoshop CS6 to merge the results and take you through the steps that we’ll
be taking to achieve our focus stack.

Method

Generally when shooting with the intention of focus stacking, it’s advised you use a tripod, as you want the two (or more) images to overlap
properly or your stack won’t work. However, if you have a relatively steady
hand then don’t worry about this too much, I’ve done all of my focus stacking
(including this example) hand-held and it works fine; Photoshop is
quite forgiving if you allow a little room to crop the uneven edges of your
photos later.

This is our focus stacking example. I'm using two pictures to keep things simple but you can use as many as you like.

Our two pictures to be used in the focus stacking process [Photo: Marie Gardiner]

As you can see, the picture on the right has a blurred flower but also elements of the spider web that are in focus that I’d like to keep.

Open your pictures into Photoshop (you can still make your
RAW adjustments if needed, just be sure to synchronise the pictures first so
the same changes are applied to both). Once opened, go to File > Automate
> Photomerge.

Photomerge in Photoshop CS6

Click ‘add open files’ and make sure ‘blend images together’
is not ticked as you want the photos to be layered on top of one another:

Photomerge options in Photoshop CS6

Press okay to create your layered images and you’ll see
Photoshop has aligned them, probably leaving some transparent or harsh, obvious
edges… don’t worry about these just yet.

Erasing blurred aspects of your image

Our two example pictures are now layered one on top of the other

You can see my two pictures in the layers panel on the right hand side and the blurred flower is on top. Have the image you want to erase blur from on top (sharp focus on the bottom layer), choose the eraser tool, change it to a soft, large brush and gently start to erase where the blurred parts are that you want sharper. It may help if you either lower the opacity of the bottom layer, or make it entirely invisible so that you can better see what you’re doing:

Our top, blurred layer is now erased in parts

It’s worth noting here that if you know how, you should do this through a layer mask instead of erasing, but to keep this tutorial straightforward I'm using the eraser in this instance.

Continue to
erase any parts that aren't in focus but were in your other shot(s). If you’re
doing this for more than two pictures, remember to work on more than one layer;
you’ll need to go through each one as demonstrated, erasing the out of focus
parts that you want to be sharp. If you find that there’s been a slightly
different exposure for each shot and you can see the erasing line once you
return the opacity to 100%, take a soft (smaller) eraser brush and lower the
opacity to 30-40% and go around the visible edges. Work outwards and keep
lowering the brush opacity until you can’t see the edge (the clone-stamp tool
may also be of use here).

Merging the layers and cropping your picture

Once you’re happy with your result, you can merge the
pictures together by going to Layer > Flatten Image:

Flatten your image in Layer > Flatten

When you have your flattened image, use the rectangular
marquee tool to select where you want the edges of your picture to be, so not
including any rough/transparent edges and then click Image > Crop.

Now make any final adjustments you feel the image may require and you’re done

My finished focus-stacked image with adjustments

In my example, I cooled off the colours a little, brought
back a few blown out highlights and gave the background bokeh a soft pop.

Conclusion

Focus stacking is very effective but is it worth the time
and effort?

Positives:

It is very useful for overcoming the shallow depth of field
problems that close up photographs can be limited by.

You can be creative with things that you couldn’t necessarily
have got at the time; selective focus for example.

If you find after shooting that your focus was slightly out
on a picture, it’s recoverable if you have a similar shot.

You can use the technique to get incredible detail from a
close, wide aperture shot.

Negatives:

It is incredibly difficult to focus-stack anything with
movement (without specialist equipment like a focusing rail), so you’ll find
yourself greatly limited if you try to do this with insects or a flower blowing
in the wind etc.

It requires a steady hand or a tripod

You need specialist software to merge your photos

If you have the appropriate software, I certainly think
focus stacking is worth a go. It’s a good skill to learn and in the right
circumstances can be incredibly effective; just don’t rely on it for the
perfect shot.